Cataracts are a common cause of poor vision and are the leading cause of blindness. There are at least 100 M eyes with cataracts causing visual acuity of less than 6/60 in meters (or 20/200 in feet). Cataract extraction is the most commonly performed surgical procedure in the world with estimates of over 22 million cases worldwide and over 3 million cases being performed annually in North America. Generally, there are two types of cataract surgery: small incision cataract surgery with phacoemulsification, and extra-capsular cataract extraction.
In small incision cataract surgery with phacoemulsification, the more common approach, about a 2 millimeter (mm) incision is made in the cornea and the opacified natural lens is removed with irrigation, aspiration, and phacoemulsification while leaving the elastic lens capsule intact to allow implantation and retention of an intraocular lens (IOL). Currently, extra-capsular cataract extraction surgery is a more invasive procedure and is performed in the developing countries where there are fewer resources. In this procedure a large incision of 6 mm or more is made in the sclera, and the complete opacified natural lens is removed.
One of the more critical components of both of these surgical procedures is the capsulorrhexis (which is also referred to as the capsulotomy), which is the incision in the lens capsule made to permit removal of the lens nucleus and cortex. The lens capsule is a transparent, homogeneous basement membrane that comprises collagen. It has elastic properties without being composed of elastic fibers. The capsule has a smooth surface contour except at its equator where zonules attach.
Typically the capsulorrhexis creates a symmetric circular incision, centered about the visual axis and sized appropriately for the IOL and the patient's condition. The mechanical integrity around the newly formed incision edge needs to be sufficient to withstand the forces experienced during cataract extraction and IOL implantation. Postoperatively, the newly formed capsule rim hardens and the opening contracts, providing further strength and structural support for the IOL to prevent dislocation and misalignment.
The current standard of care for capsulorrhexis is Continuous Curvilinear Capsulorrhexis (CCC). The concept of CCC is to provide a smooth continuous circular opening through the anterior lens capsule for phacoemulsification and insertion of the intraocular lens, minimizing the risk of complications including errant tears and extensions. Currently, the capsulorrhexis is performed manually utilizing forceps or a needle. This technique depends on applying a shear force and minimizing in-plane stretching forces to manually tear the incision. One complication that may develop when performing a capsulorrhexis in this manner is an errant tear. Errant tears are radial rips and extensions of the capsulorrhexis towards the capsule equator. If an errant tear encounters a zonular attachment the tear may be directed out to the capsular fornix and possibly through to the posterior of the capsule. Posterior capsule tears facilitate the nucleus being “dropped” into the posterior chamber, resulting in further complications.
Further problems that may develop in capsulorrhexis are related to inability of the surgeon to adequately visualize the capsule due to lack of red reflex (reddish reflection of light from the retina), to grasp it with sufficient security, or to tear a smooth symmetric circular opening of the appropriate size. Additional difficulties may relate to maintenance of the anterior chamber depth after initial opening, small size of the pupil, or the absence of a red reflex due to the lens opacity. Additional complications arise in older patients with weak zonules and very young children that have very soft and elastic capsules, which are very difficult to mechanically rupture.
Following cataract surgery there is a rapid 1-2 day response where the capsule hardens and capsule contraction starts. This contraction continues over a 4-6 week period where fibrosis of the capsulorrhexis and IOL optic interface and of the IOL haptic and capsule interfaces also occurs. Even beyond one year the capsule continues to contract to a lesser degree. Thus positioning the capsulorrhexis is a critical factor in the long-term success.
Accordingly, there is a need in the art to provide new ophthalmic methods, techniques and devices to advance the standard of care for capsulorrhexis.